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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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100                                 ALASKAN GLACIER STUDIES
The most remarkable feature in the transformation of Haenke Glacier was the advance of its front completely across the fringing alluvial fan to the sea. At the same time it expanded laterally, as Turner Glacier does, with two wing-like ends, one pointing northward, the other southward. The latter wing coalesced with the north wing of Turner Glacier, thus forming a continuous ice cliff from the southern tip of Turner Glacier to the northern end of Haenke Glacier, adding nearly a mile and a half (PI. XXXVI) to the ice qliff that had existed here ten months earlier. Although this new ice front was completely tidal there was not an active discharge of icebergs from it, possibly because of the fact that the front stood in very shallow water, resting on alluvial deposits previously laid down by the glacial stream that formed the destroyed alluvial fan. Some icebergs were being discharged, however, and the glacier front was everywhere a steep cliff; but for the most part it was so stained by the black shale moraine that clear ice appeared in it only in small patches where fragments had recently fallen (PI. XL, B).
The forward movement of Haenke Glacier carried its front at least 4500 feet farther out than it had stood ten months before (PL XXXVI), and the terminus of this glacier experienced a much greater actual forward movement than any of the glaciers that advanced in 1906, but not nearly so great as the Hidden Glacier between 1906 and 1909. This greater forward thrust of the front may be due entirely to the difference in conditions surrounding the terminus. The other three advancing glaciers, the Marvine, Atrevida and Variegated (and also the Galiano) terminate in expanded piedmont ice bulbs in which the movement, thickening, and breakage resulting from the thrust dissipated itself without accomplishing a large measure of forward motion of the glacier fronts; but Haenke Glacier (and also the Hidden) had no such expanded bulb, and the thrust, even though of less degree, being concentrated on a front only slightly broader than the valley glacier itself, naturally pushed it forward. It is to be pointed out, however, that a part of the advance of Haenke Glacier may be only apparent, for it is possible that a stagnant ice mass underlay the fringing alluvial fan; but we have no proof that this was so.
Haenke Glacier from 1909 to 1913. Like the Atrevida Glacier, the Haenke since 1906 had been so healed by ablation that from a distance one would not, in 1909, have suspected that it had so recently been broken into impassable condition. The spasmodic advance cannot, therefore, have lasted much longer than the summer of 1906, if indeed it had not ceased by that time. All the crevasses were hidden and the surface was once more completely covered from side to side from the front far up into the valley, with a uniform sheet of black shale ablation moraine. The surface was, perhaps, somewhat more hummocky than in 1905, though it is impossible to prove this from the photographs, in which the condition of 1905 and 1909 seem almost the same, though in each year vastly different from the condition in the intermediate period of 1906.
The front of the glacier was apparently not so far out as in 1906, and it certainly was no longer tidal (PI. XLI, B); but it still possessed a debris-stained cliff throughout practically its entire front. At the base of t.Tiia cliff numerous debris cones and some small alluvial fans had formed, the former where moraine had slid down the ice front, the latter where streams emerged from the glacier. There were no appreciable changes between 1909, 1910, and 1913. The short time that the glacier was tidal is proof of the conclusion reached in 1906 that the ice cliff rested in shallow water. It seems safe to predict that the present cliff will soon disappear as the result of ablation, and that an extensive alluvial fan will eventually again develop and fringe the glacier front. The